|What is the model of your Compaq computer ?|
If you're not sure, it's on a stuck on Compaq or HP supplied label, probably on the outside of the computer case somewhere.
Is the hard drive SATA or IDE ?
A hard drive that is new, or a used hard drive that has had it's data deleted, has no data and no operating system on it.
If the bios does not find an operating system while booting, you get a message from the bios that nothing bootable was found, or similar
What disk did you make ?
What does it have on it ?
Is it a DVD ?
The bios settings must be set so whatever disk with an operating system on it you want to boot from is before the hard drive, in the Boot Order or similar settings.
If you have a laptop, you usually also have the option of pressing a key, while a line is on the screen while booting, that allows you to select one drive to boot the computer from.